These instructions apply to the BMW 2 Series Mk2 (G42) 2021-present.
For other models, please choose your vehicle here.
On the BMW 2 Series (G42, 2021–present) the 12 V battery isn’t under the bonnet — it lives in the boot, under the luggage floor. Disconnect it in the right order and your settings come back cleanly.
Like most modern BMWs, the G42 2 Series carries its 12 V battery in the boot rather than the engine bay — a packaging choice that helps weight distribution but catches out owners expecting to find it under the bonnet. You’d disconnect it to fit a fresh battery, to isolate the electrics before doing bodywork or audio work, before a long lay-up, or after a jump-start recovery. Done in the correct order, the car wakes up and relearns its settings without drama. The steps below cover the standard 12 V job that any owner can do; the one thing to keep in mind is that certain models add a second, higher-voltage system that is strictly hands-off.
Where the 12 V Battery Is
Open the boot and lift the luggage-compartment floor panel. The 12 V battery sits beneath it on the right-hand side, usually under a fabric or foam cover. There is a remote jump-start positive post in the engine bay (marked +) for boosting a flat car, but the battery itself is in the boot. On the terminals, the negative clamp is the black one marked with a minus (−) and bonded to the body earth; the positive is the red one, usually under a cover. Identify both before you start.
Getting Ready
- Make sure the car is fully off — not in READY — and take the key fob away so the car can’t wake up.
- Switch off the lights, climate, iDrive and any accessories, and close the doors.
- Note that the infotainment and comfort settings live in memory that a disconnection can disturb, so be ready to reset the clock and a few preferences.
- Wait a couple of minutes after switching off so the modules power down before you pull the terminal.
- Wear gloves and eye protection and have the right spanner ready — typically a 10 mm for the clamp.
This is a common job.
Disconnecting
- Switch everything off, remove the key and wait a couple of minutes.
- Lift the boot floor, fold back the cover and slacken the negative (−) terminal first; move it clear and tuck it aside so it can’t spring back.
- Release the positive (+) clamp only if you’re removing the battery — fold back its cover first and keep the spanner off surrounding metal.
- If you’re lifting the battery out, release the hold-down and disconnect the vent tube where fitted, then lift it clear.
Reconnecting
- Refit the battery, hold-down and vent tube if you removed them.
- Fit positive first, then negative, and tighten both firmly.
- Refit the covers and floor panel, switch the ignition on, correct the clock, then start.
A Note on Mild-Hybrid Models
The 220d mild-hybrid has a separate 48 V system — leave that to a workshop. The owner-serviceable 12 V battery in the boot is what’s covered here; never touch the 48 V components or their cabling. If in any doubt about which battery you’re looking at, stop and check — the standard 12 V unit is the one under the luggage floor.
What You’ll Need to Reset Afterwards
- Clock and radio — reset the time and re-store your presets once power returns.
- Tyre-pressure monitoring — re-store your tyre pressures so the system has a fresh baseline.
- Service indicator (CBS) — make sure the clock and date are right, as the Condition Based Servicing clock relies on them before any service reset.
- Windows and comfort settings — some one-touch and personalisation settings may revert and need setting again.
- A few messages may appear briefly on first start and clear once the car has been driven a short distance.
If a Warning Light Stays On or the Car Feels Off
- Check both terminals are properly tight — a loose clamp in the boot is easy to under-tighten and causes intermittent faults.
- Drive the car a short distance to let the modules relearn; many messages self-clear.
- Re-do the window and comfort settings if they didn’t survive.
- Rule out a genuinely flat or aged battery, which can throw lights of its own.
- Read any stored code if a light persists after a drive.
Registering or Coding the New Battery
Yes. This car has a battery-monitoring system, so a replacement battery must be registered — the car needs to know it is new, or it under-charges it and the fault stays logged. Registration is done through the OBD port with a compatible diagnostic tool (a specialist or dealer, or a capable aftermarket scanner); there is no owner button sequence. Replace like-for-like (AGM for AGM, EFB for EFB).
Frequently Asked Questions
Where is the battery on a BMW 2 Series (G42)?
In the boot, under the luggage-area floor on the right-hand side. Lift the floor panel and its cover to reach it. There’s also a jump-start positive post in the engine bay for boosting, but the battery itself is in the boot.
Which terminal first?
Negative (−) off first, then positive if you’re removing the battery. Reconnect in reverse — positive (+) on first, negative last — and tighten both. This order keeps you from shorting the live positive to the surrounding metal.
Does a new battery need coding?
BMW recommends battery registration so the charging system matches the new battery — the car runs without it, but registering preserves battery life and keeps the charging strategy correct. It’s a quick step with the right tool and is worth doing when the battery is replaced.
Is it safe on the mild-hybrid?
The 12 V job in the boot is fine for an owner. Never work on the orange 48 V cabling or components on the mild-hybrid — that’s a workshop task. Stick to the 12 V battery under the luggage floor and you’re on safe ground.
What resets when I disconnect it?
The clock, radio presets, tyre-pressure baseline and some comfort or one-touch settings typically need re-doing. None of it is permanent — it’s all quick to set back up, and warning messages generally clear after a short drive.
Can I jump-start it instead?
Yes — use the engine-bay positive post and a body earth point with jump leads or a booster pack. If the battery is only flat and you want to get going, jump-starting avoids losing your settings. Disconnect only when you’re renewing the battery, storing the car or doing electrical work.
If a fault light stays on afterwards, check the code on autodtcs.com.
Independent guide — not affiliated with BMW. Always follow your official service manual and safety precautions. Read our full disclaimer.